Ltk is a Common Lisp interface to the well known Tk graphics toolkit. Tk is probably the graphics toolkit that has been ported to the most platforms. Ltk gives a true Lisp interface to Tk. Every widget is a CLOS object on the Lisp side - so using it is very natural. You can even subclass all widgets to create your custom versions of them.
Ltk is written in portable Common Lisp, so it runs under almost any operating system/lisp system combination.
Your Ltk applications run everywhere! Ltk is stable and actively maintained.